Pre-filled hypodermic syringes provide several advantages for the home-use market. These advantages include the fact that pre-filled syringes can be prepared for each fluid medicament with the exactly required dosage. Further, they are easily operated, by merely advancing the stopper of the syringe. Aside from the costs of the particular medication that is being used, pre-filled syringes are also economically manufactured. A consequence of all this is that pre-filled syringes have commercial appeal. Nevertheless, pre-filled syringes also have a significant drawback in the marketplace. Specifically, many users are either frightened by an exposed needle or feel they are inherently incapable of performing an injection.
Because of aversions to exposed needles, as well as the many health and safety issues that may be involved, various needleless injectors and other devices have been developed for the specific purpose of concealing needles from the user. Typically, for devices where hidden or protected needles are employed, the devices are spring-operated and tend toward the use of cartridges, rather than the use of pre-filled hypodermic syringes. For example, U.S. Pub. No. 2007/0021720A1 which was filed for an invention entitled “Injector”, discloses such a device employing a variety of spring activated mechanisms. When springs are employed, however, the forces cannot be varied from application to application. This can be particularly problematic in situations where it may be desirable to use a same device, at different times, to inject different medications, with different fluid viscosities. Indeed, it may not be possible to use a same spring-loaded injector for different medications. The situation can become further complicated when consideration is given to the fact that, in a single injection procedure, the optimal force for inserting a syringe needle into a patient may be quite different from the force required to subsequently expel fluid medicament from the syringe. Furthermore, the starting force of a spring will differ from the ending force. And, this can be problematic for assuring a complete drug delivery.
In light of the above, it is an object of the present invention to provide a system using disposable cassettes that are pre-loaded with pre-filled syringes to hide the syringe needle during its use. Another object of the present invention is to provide a system for injecting fluid medicaments into a patient that uses different motors to accommodate different force requirements during an injection procedure. Still another object of the present invention is to provide a system for injecting a fluid medicament to a patient that is easy to assemble, is simple to use, and is comparatively cost effective.